Stack Smashing Detected at End of Program - c

Question

I am currently testing a program on a smaller scale to distinguish a problem when I attempt to exit the program by return 0; at the end of the main function.
Main.c
#include <stdio.h>
#include <stdlib.h>
#include "Header.h"
int main (void)
{
int i;
int Fin = 0;
Student sStu;
Array aAry;
Student *Stu = &sStu;
Array *Ary = &aAry;
InitArray(Ary, 1);
while(Fin != 2)
{
printf("Please choose a selection.\n");
printf("1. Add Student\n");
printf("2. Print Students\n");
printf("3. Exit\n");
scanf("%d", &i);
switch(i)
{
case 1:
{
AddStudent(Stu, Ary);
break;
}
case 2:
{
for(i = 0; i < Ary->Size; i++)
{
printf("%s %d\n", Stu[i].Name, Stu[i].IDn);
}
break;
}
case 3:
{
return 0;
}
}
}
}
Header.h
#ifndef HEADER_H_
#define HEADER_H_
typedef struct student
{
char Name[30];
int IDn;
}Student;
typedef struct array
{
Student *Student;
size_t Used;
size_t Size;
}Array;
void InitArray(Array *Ary, int InitSize);
void AddArray(Array *Ary);
Student AddStudent(Student *Stu, Array *Ary);
#endif
Grade.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "Header.h"
void InitArray(Array *Ary, int InitSize)
{
Ary->Student = malloc(InitSize * sizeof(Student));
Ary->Used = 0;
Ary->Size = InitSize;
memset(&Ary->Student[0], 0 , sizeof(Student) * InitSize);
}
void AddArray(Array *Ary)
{
Student Stud;
if(Ary->Used == Ary->Size)
{
Ary->Size *= 2;
Ary->Student = realloc(Ary->Student, Ary->Size * sizeof(Student));
}
strcpy(Ary->Student[Ary->Used].Name, Stud.Name);
Ary->Student[Ary->Used].IDn = Stud.IDn;
Ary->Used++;
}
Student AddStudent(Student *Stu, Array *Ary)
{
int i;
printf("\nStudent ID numbers cannot be the same!\n");
printf("Please enter the student's name: ");
scanf("%s", Stu[Ary->Used].Name);
printf("Please enter the student's ID Number: ");
scanf("%d", &Stu[Ary->Used].IDn);
AddArray(Ary);
printf("\n");
return;
}
At the end of the file, when I try to return 0; I get this error:
* stack smashing detected *: ./a.out terminated
Segmentation fault (core dumped)
When I use valgrind, I get this output:
==9966== Invalid write of size 1
==9966== at 0x402C6C3: strcpy (in /usr/lib/valgrind/vgpreload_memcheck-x86-linux.so)
==9966== by 0x8048687: AddArray (in /home/ctj0033/CSCE_1040/Homework/2_Homework/2_Test/a.out)
==9966== by 0x804874B: AddStudent (in /home/ctj0033/CSCE_1040/Homework/2_Homework/2_Test/a.out)
==9966== by 0x804881C: main (in /home/ctj0033/CSCE_1040/Homework/2_Homework/2_Test/a.out)
==9966== Address 0x41f804c is 0 bytes after a block of size 36 alloc'd
valgrind terminates due to an fatal error during my attempt to exit my program.
It only happens at the end and I can print the contents of the struct array properly. I have looked into realloc(); since I am fairly sure the error lies within that, however I am uncertain precisely what I have done wrong. I have attempted to alter the way I allocate the memory in InitArray(); and the way I use realloc(); but to no avail.
What have I done wrong?

Answer 1

Your immediate problem is that you're trying to use an "invalid pointer". (Actually, it's a completely valid pointer, it just points to a wrong place)
sStu is a Student, and Stu is a pointer to it. But when you add your second student, you write to Stu[1] - which is the space after sStu. Most likely there's something else in this space, so when you write to Stu[1], you overwrite something else. (It's unpredictable exactly what will be in that space.)
It looks like you want to use Ary->Student everywhere you have Stu.
(If you do that, you might find some more problems - such as the fact that you check if you need to expand the array after writing to the next element)